1. Field of the Invention
The present invention relates to a driving method for liquid crystal display (LCD) panels, and in particular to a method for driving LCD panels by alternately displaying a dimmed image and a normal image in a single frame so that image display performance on LCD panels can be brought closer to the impulse approach used in cathode ray tube (CRT) displays, and the flickering phenomenon can be significantly rectified.
2. The Related Art
One effective method of improving the video display performance of and correcting the usual after-image phenomenon on LCD panels is to use pseudo-impulse drive (PID) technology, which enables the digitized image to more closely approach the performance of the impulse-emission of the CRT displays. Referring to FIGS. 1A-1C, the current method of pseudo impulse drive employs alternate display of a normal image 10 and an all-black image 20 to emulate the impulse emission of the CRT.
FIG. 5 shows an LCD panel 34 having multiple data lines connected to multiple data line drivers 31 and multiple gate lines connected to two gate line drivers 32, 33 for displaying a digitized image. A pixel in the digitized image is displayed in an overlapping area between a data line and a gate line. A selection rule is defined for selection from at least two gate line drivers of the PID, one of which is selected as the first gate line driver and the other as the second gate line driver so that the first and second gate line drivers alternately output a normal image 10 and an all-black image 20 in a single frame.
The first gate line driver starts to scan from the first line to the eleventh line one line at a time sequentially downward, as shown in FIG. 1A, to produce a normal image 10, and the second gate line driver starts to scan from the 241st line down to the 251st line sequentially downward, as shown in FIG. 1B, to produce an all-black image 20 until the bottom is reached. Thereafter, the first gate line driver then continues with the normal image 10 from the 241st line, and the second gate line driver then continues with the all-black image 20 from the 1st line as shown in FIG. 1C, and the line scanning proceeds in such a manner until all gate lines connected to the first and second gate line drivers are used, thus emulating a full sweep across the display screen.
As shown in FIG. 1C, before part of the normal image 10 is displayed, the gate lines starting from the 241st line were first used to display part of an all-black image 20 as shown in FIG. 1A, so the drive voltage of all pixels on the 241st line and following lines has been restored to non-emission state after the all-black image 20. Therefore, when the first gate line driver starts the line scanning from the 241st line to produce part of the normal image 10, the pixels of the 241st line and lines following undergo a voltage change very much like the impulse emission of the CRT, to more closely emulate the impulse drive of the CRT.
However, if the refresh rate of the LCD panel is only 60 Hz, using the above PID method to drive an LCD panel, the high-speed switching between all-black images 20 and normal images 10 could easily produce flickering phenomenon to the human eyes. Further, the all-black image 20 could be inserted before the normal image 10, thus affecting the brightness of the LCD panel by as much as 50%. Therefore, if the conventional PID method is used to drive an LCD panel, it is necessary to use a backlight source of higher luminescent efficiency.